First you have to take out the shield generators. Lots of nasty rocks to fly through. Have your wingmen handle the TIEs but fly straight through (past the tri-light objects) to the large shield. Use your ion cannons to blast 3 of them away.

Next, bomb the turrets to stop them. They're the tiny things firing at you :) You're not very agile so be careful. There will be a group around the prison and then more around the armory. On the way to the 3rd spot blow up the dome near a satellite dish to get cluster missiles! Then even more around the comm setup before you bomb the actual relays.

Your radar will light up, follow the orange cone. You can cut corners if you want, just make sure you get to the train's destination. Take out the turrets and wait for it to load up.